Dependence of Viscosity on Concentration or Temperature

The transition from the isotropic to the nematic state is marked by a decrease in the shear viscosity (Hermans 1962 Gillmor et al. 1994) (see Figs. ll-4a and 11-5). This is not surprising, since molecules can slide past each other more readily in the nematic state than in the isotropic state. However, since the nematic is accessed from the isotropic state by an 

For lyotropic LCPs, there is a hiphasic window of concentrations over which nematic and isotropic phases coexist, t he polymer concentrations in the coexisting isotropic and nematic phases are designated by C (or = Trd Lv /A) and Cj (or (pj = jrd Lv2/A), respectively. There is also a theoretical concentration C, at which the isotropic phase becomes unstable to orientational fluctuations. According to the Onsager theory, 02/0 = 1.047 and 02/0i = 1.27 (see Section 2.2.2). Thermotropic LCPs often have a biphasic window of temperatures over which isotropic and nematic phases coexist. This biphasic window exists in nominally single-component thermotropics because of polydispersity the nematic phase is typically enriched in the longer molecules relative to the coexisting isotropic phase (D Allest et al. 1986). 

---